The present invention is directed to a technique for bonding soft biological tissue to close an incision therein and, in particular, to heating of the tissue with high frequency electric current in combination with compression of the tissue.
For purposes of the ensuing discussion, soft biological tissue will be referred to just by the term xe2x80x9ctissuexe2x80x9d for reasons of simplicity and economy of space, and should be understood to mean any tissue other than bone, such as skin, organs, blood vessels and nerves. When tissue is injured, it must be repaired by re-joining the edges of tissue that has been torn or cut. For example, when tissue is cut during a surgical operation, the incision(s) must be closed to complete the surgery. In fact, a tissue break (particularly in blood vessels) may also need to be closed even during surgery, such as to provide hemostasis, namely to control bleeding. Every cut, puncture or break in tissue due to any reason is referred to herein generically as an xe2x80x9cincisionxe2x80x9d.
Many techniques are known for closing an incision. Some of these techniques are suturing, clamping, stapling and gluing. These techniques have a number of well known disadvantages which include one or more of the following: leaving a foreign body in the tissue, pinching of tissue which can cause delayed healing and/or inflammation, allergic reaction, limited applicability, complexity of use, and the need for expensive equipment.
Other techniques of connecting blood vessels use laser radiation, heated tools and the passing of high frequency current directly through the parts of tissue being connected. All the above mentioned methods employ the phenomenon of tissue albumen denaturation caused by heating. When the temperature exceeds 55xc2x0 C. the denaturation causes albumen coagulation. The globular molecules of albumen become straightened and entangled among themselves. If two edges of tissue are connected and heated the entanglement of albumen molecules results in their bonding. The higher the temperature, the faster and better is the coagulation. However, at temperature exceeding 100xc2x0 C. the tissue becomes dehydrated, its electric resistance increases, which leads to further temperature rise and charring of the tissue.
Quite a number of research efforts have been published on laser techniques in blood vessel surgery. Still this technique has not been accepted for general clinical use because of the technical complexity of its utilization and because of inadequate surface energy release. As to employment of high frequency current for heating tissue, the technique is widely used in surgery for hemostasis.
In tissue bonding, as with suturing for example, the separated tissue edges must be rejoined to facilitate healing. The joint should be relatively strong, it must promote healing and minimize if not eliminate any problem which interferes with healing. However, the use of the existing bipolar devices for connecting soft tissues other than walls of compressed blood vessels encounters insurmountable difficulties. Specifically, it has been difficult to correctly set the electrical signal parameters to achieve such aims. This is due, at least in part, to the fact that tissue has an electrical resistance which can vary widely depending on many factors such as tissue structure and thickness as well as the tool/tissue contact area which is not controlled in any way. If too little current is applied, then the tissue joint can be spongy, weak and unreliable. On the other hand, if too much current is applied, then the working surface of the electrode can stick to the tissue so that removal of the electrode causes bleeding and possible injury. Also, the tissue in the overly-heated zone can become desiccated and charred. Therefore, such high frequency coagulative devices have seen limited use for only hemostasis of blood vessels of relatively small diameter. These devices have not been used for replacing the well known above-mentioned means for bonding tissue (xe2x80x9cbondingxe2x80x9d is used in the sense of closing incisions to facilitate healing), such as suturing, stapling, etc. even though their use is not subject to the above-mentioned disadvantages of such means for bonding tissue.
Two types of tools are used for high frequency electrocoagulation, namely mono-polar and bipolar. The discussion below will be limited solely to bipolar devices which provide an electric current flow within the tissue volume clamped between the electrodes.
Use of bipolar devices to close incisions in tissue which must be healed will be appreciated as presenting quite a challenging task because the amount of damaged tissue, such as due to charring or other healing-delaying effects, must be minimal and not very deep, and xe2x80x9covercoagulationxe2x80x9d must be avoided. Prior art techniques have been proposed to determine the degree of coagulation based on the electrical impedance of the tissue. The relationship between electrical tissue impedance over time and coagulation is described in the article xe2x80x9cAutomatically controlled bipolar electrocoagulationxe2x80x9d by Vallfors and Bergdahl, Neurosurgery Rev. 7 (1984), pp. 187-190. As energy is applied to the tissue, the impedance decreases until it reaches a minimum value. If current continues to be applied, the authors describe imprecisely that the tissue begins to dry out due to the heat generated therein, and the impedance rises. Unless the heating is stopped, severe tissue damage will occur. Thus, the Vallfors and Bergdahl technique provides for determination of the instant of occurrence of the impedance minimum and then stops the current flow a preset time thereafter. U.S. Pat. 5,403,312 also utilizes this phenomenon to monitor the impedance, change in impedance and/or the rate of change in impedance to determine whether it is within a normal range. However, these techniques are typically applied to blood vessel coagulation. Usage of these techniques for other types of tissue creates severe difficulties due to the wide variation in values of impedance which can be encountered due to, for example, tissue structure, thickness, condition of the tissue and condition of the tool surface.
One object of the present invention is to provide an improved bipolar electrocoagulation technique for bonding tissue with heat energy created by high frequency electrical current passed therethrough between electrodes.
Another object of the invention is to prevent sticking of the electrodes to the tissue.
A further object of the invention is to achieve a stronger bond.
Yet another object of the invention is to prevent burning of tissue in the bipolar electrode zone.
One other object of the invention is to provide a consistently good tissue bond regardless of differences in tissue structure and thickness.
Still another object of the invention is to bond tissue to close an incision quickly and reliably.
Another object of the invention is to bond tissue in a way which promotes fast healing.
A further object of the invention is to rely on measurement of tissue impedance to accurately control the degree of coagulation which bonds the tissue for a wide variety of different tissues.
Yet another object of the invention is to design the electrodes such that they can function as an effective heat sink for the heated tissue with which they are in contact. Another object of the invention is to design the electrodes to maintain uniformity in the area of electrode/tissue contact.
These and other objects are attained in accordance with one aspect of the present invention directed to a method and apparatus for bonding soft biological tissue having an incision therein with forceps adapted to grip a portion of the tissue on both sides of the incision. Electrodes are provided for contacting the tissue portion. An electrical power source provides a high frequency electrical signal to the electrodes to be passed through the tissue portion, and the electrical power source is controlled to provide the electrodes with one voltage signal during a first of two stages, and another voltage signal during a second of the two stages.
Another aspect of the present invention is directed to a method and apparatus for bonding soft biological tissue having an incision therein with forceps adapted to grip a portion of the tissue on both sides of the incision. Electrodes are provided for contacting the tissue portion. An electrical power source provides a high frequency electrical signal to the electrodes to be passed through the tissue portion, and a clamping means applies force with the forceps to compress the tissue portion, such force being set to different levels in two time periods, respectively, while the high frequency electrical signal is being passed through the tissue portion.
Another aspect of the present invention is directed to a method and apparatus for bonding soft biological tissue having an incision therein with forceps adapted to grip a portion of the tissue on both sides of the incision. Electrodes are provided for contacting the tissue portion. An electrical power source provides a high frequency electrical signal to the electrodes to be passed through the tissue portion, with a constant voltage level of the signal being provided during at least a portion of a time period when the high frequency electrical energy is passed through the tissue portion, and the constant level being modulated by a low frequency signal.
Another aspect of the present invention is directed to a method and apparatus for bonding soft biological tissue having an incision therein with forceps adapted to grip a portion of the tissue on both sides of the incision. Electrodes are provided for contacting the tissue portion. An electrical power source provides a high frequency electrical signal to the electrodes to be passed through the tissue portion. The electrodes are dimensioned relative to size of the tissue portion to be an effective heat sink for conducting heat away from the tissue and thereby prevent sticking of tissue to the electrodes.
Another aspect of the present invention is directed to a method and apparatus for bonding soft biological tissue having an incision therein with forceps adapted to grip a portion of the tissue on both sides of the incision. Electrodes are provided for contacting the tissue portion. An electrical power source provides an electrical signal to the electrodes to be passed through the tissue portion. The impedance variation in the tissue portion as a function of time, while the electrical signal passes through the tissue portion, is predetermined to provide a preselected impedance value. The impedance is measured to provide a measured impedance signal as a function of time, while the electrical signal passes through the tissue portion, and the electrical signal is stopped from being passed through the tissue portion when a value of the measured impedance signal reaches a preset impedance value relative to the preselected impedance value, with the preselected impedance value being specific in particular to the biological tissue being bonded.
Another aspect of the invention is directed to a method and apparatus for bonding soft biological tissue having an incision therein with forceps adapted to grip a portion of the tissue on both sides of the incision. Electrodes are provided which are adapted to contact the tissue portion in an electrode/tissue contact area. An electrical power source provides a high frequency electrical signal to the electrodes to be passed through the tissue portion. The electrodes are dimensioned relative to size of the tissue portion to maintain uniformity in the electrode/tissue contact area.